Everyone who has been infected by Covid-19 and are already vaccinated twice are asking—what about booster shots?
Many countries believe that the benefits of the first two doses might be wearing off so they’re looking for a third shot to further boost our anti-viral capabilities against Covid-19, especially the Delta variant. But is it really needed? Aren’t two doses enough to protect us from severe disease and hospitalization?
An expert’s look
Dr. Nina Gloriani, chair of the Vaccine Expert Panel (VEP) of the Department of Science and Technology (DOST), explained that there is a “primary” series of vaccines, comprised of two to four doses, that are needed to reach full effectiveness, like for the Covid-19 vaccines. There’s also a “booster” dose, which can be given months or years after the primary dose to “refresh the immune system’s memory and maintain protection.” For Covid-19, the booster is the third or additional dose to the primary series.
She pointed out that the need for booster shots after the primary series will depend on the duration of the immunity, whether months or years. “If immunity is short lived and the magnitude of the antivirus in the body is smaller, definitely it will need booster shots.”
The boosters, she said, will serve as the secondary immune response to help the antivirus level become more pronounced or with a higher number. Protection is longer in duration and response is stronger and becomes more effective in limiting infection.
Dr. Gloriani pointed out that the antibodies come from the so-called “B cells,” and the level of antibodies that a person gets depends on the number of B cells that later divide into plasma cells to create the antibodies, which is called “clonal expansion.” The B cells will recognize the antigens, and it will then be activated to “clonally proliferate,” which means it will multiply in numbers.
“What we have seen is more B cells clonally expand with time and with longer interval between doses. So, more plasma cells will be there and divide to produce more antibodies. As time passes, there is what is called ‘affinity maturation,’ where the antibodies will bind to the viral antigen. And as more antibodies are produced with stronger affinity, therefore, there is wisdom in waiting for the right time to boost,” Dr. Gloriani said.
But the big question remains: “To boost or not to boost?”
There are considerations if a boost is really needed, she said, like “waning immunity.” What should be looked at also when thinking of booster shots are the risk groups like the elderly, the immunocompromised, and those with risks of higher exposure like those who care for Covid-19 patients and the medical frontliners. There is also a need to look at the epidemiology of breakthrough cases over time, disease severity if there are variants, or data on vaccines on how their third dose will perform or have performed. To be looked at as well, she said, is the safety and immunogenicity—did the antibodies multiply, or, is the third dose safe? Or can there be “mix and match,” or can lower doses be given as boosters?
So, what is the optimal timing for boosters? Should it be six, eight or 12 months after the primary series? The World Health Organization (WHO), however, said that the scientific justification for boosters remain unclear, although WHO Director-General Dr. Tedros Adhanom Ghebreyesus acknowledged third doses “might be necessary for at-risk groups.” He added, however, that “they do not want widespread use of boosters for healthy people who are fully vaccinated.”
Dr. Tedros also called on countries to “prioritize vaccinating the most at-risk people around the world who have yet to receive their first dose.”
Are Covid-19 boosters effective and safe?
Dr. Marie Carmela Lapitan, professor, Institute of Clinical Epidemiology of the UP Manila National Institutes of Health (NIH) cited the findings of the Covid-19 Living Clinical Practice Guideline (CPG) Task Force, saying that rather than looking at antibodies, what needs to be considered is whether they want to prevent infection or give additional protection. She cited only two observational studies that provided actual clinical outcomes after a booster. Both studies used the Pfizer vaccine and were done in Israel.
The first study showed that the margin of protection against the virus was recorded at 84 percent 14 days after the booster was administered compared to the one not given a booster. The second study showed that receiving a booster provided an 11.4-fold protection against Covid-19 infection, and an even higher 15.5-fold protection against severe disease.
So to answer the question above, Dr. Lapitan said the studies reporting the safety outcomes at least 28 days after receiving the boost indicate that the adverse reactions were mostly mild and transient between those who received the boost and those who did not. When the primary vaccination and the booster shots were compared, some reported similar while some reported lower rates of reaction.
For the severe and serious adverse events, the studies revealed very low rates or even no adverse events, says Dr. Lapitan, adding that majority, if not all, were unrelated to the boosters. For the immunocompromised, there was no acute rejection among transplant patients who received the boosters.
But what if the booster vaccine is different from the primary vaccination? She said that the three studies that looked at this showed that heterologous booster vaccination was associated with higher local and systemic reactions, but these were generally mild and moderate adverse events.
Now, about the certainty of the evidence that these studies provided on a general population scale, Dr. Lapitan said they had to downgrade expectations since most of the studies were observational, and those that conducted the randomized trials, most of them only showed immunogenic and not clinical outcomes.
She said of the 21 studies conducted on Covid-19 vaccine efficacy, effectiveness and safety, they showed that Covid-19 boosters are effective in preventing Covid-19 infection, but based on very low to low certainty of evidence. Boosters were also declared safe based on moderate-certainty evidence.
However, Dr. Lapitan cited as well other evidence that will help in the decision-making process of whether to roll out Covid-19 vaccine booster programs. The WHO conducted systematic reviews that included 50 reports that consist of real-world evidence of primary vaccination, how are they working.
It showed that majority of vaccines showed 85 percent effectiveness against any infection, and 90 percent against severe disease. As for the vaccines’ capacity to fight other variants, it showed 85 percent effectiveness against any infection and 90 percent against severe disease with the Delta variant. Also, all vaccine types showed 85 percent effectiveness against severe disease.
As to the vaccines’ effectiveness over time, during this stage that many nations, including the Philippines, consider giving boosters, the reviews showed that vaccines showed 80 percent effectiveness against any infection and a high 90 percent effectiveness against severe disease even later after a longer interval from the time the primary vaccination was given.