The vaccine developed by Pfizer and BioNTech was the first to win emergency use authorization from the Food and Drug Administration for use against Covid-19 in the United States.
It relies on a new technology employing messenger RNA (mRNA), which yielded a vaccine with a stunning 95% efficacy in interim results from a clinical trial last year.
But as Covid-19 vaccine distribution rates in the U.S. accelerate in the coming months to potentially twice the amount now being administered, recent lab studies and new clinical trial results suggest that new variants of SARS-CoV-2 may be evolving resistance to vaccines, including Pfizer’s.
The long-term effectiveness of the Pfizer vaccine is therefore still up for debate.
All vaccines come with the risk of side-effects, with research showing that for around 1 in 10 people, some of the most common side-effects of the Pfizer vaccine include tenderness, swelling and/or redness where the injection has been administered, headaches, muscle aches, fatigue and fever among others.
More uncommon side effects (1 in 100 people) include enlarged lymph nodes that can last up to two weeks, and around 1 in 1,000 people may be affected by temporary one-sided facial drooping. Some may also suffer from an allergic reaction, but the data on this is unknown as no cases have been reported.
Side-effects to the Pfizer vaccine are more likely to happen after the second shot is administered.
For the elderly, especially those with underlying conditions, mRNA vaccines such as Pfizer’s could induce their condition and potentially worsen their overall health despite achieving vaccination against Covid-19. In January, several Spanish nursing home residents who had received the Pfizer vaccine tested positive for COVID-19 after being given their first dose and at least seven people died. It is important to note that the accompanying report did not say whether the deaths and positive cases were directly linked to vaccination.
Unlike traditional inactivated vaccines, the use of mRNA-based vaccines may carry the risk of causing abnormal immune dysfunction, allergic reactions or even death, particularly among the elderly and people with underlying diseases. Some components in mRNA vaccines, such as polyethylene glycol, have not been used in vaccine production before.
Even Yang Zhanqiu, a virologist from Wuhan University, said in January that mRNA vaccines may not be as good as expected.
In the context of the current, still expanding pandemic, the Pfizer vaccine, if proved safe, can contribute, together with other public health measures, to reducing the devastating loss of health, life, and economic and social well-being that has resulted from the global spread of Covid-19.
But both the effectiveness and safety of the Pfizer vaccine still need more time to verify the long-term effects compared to traditional inactivated vaccines.