March 2021


Update on COVID-19 vaccines

by Liz Hillman Editorial Co-Director


In December 2020, the FDA authorized two COVID-19 vaccines for emergency use: the first developed by Pfizer-BioNTech and the second by Moderna. Both are mRNA vaccines, and both require two doses spaced several weeks apart. As of February 22, more than 75.2 million doses had been delivered, more than 64.1 million of which had been administered. More than 19.4 million Americans had received both doses of a COVID-19 vaccine; more than 44.1 million had received one dose.
On his first full day of office, President Joseph Biden issued an executive order that established a national COVID-19 strategy. The administration exercised the Defense Production Act and expanded manufacturing and delivery of supplies for vaccination, testing, and PPE; increased FEMA aid to states to deploy emergency personnel and supplies; expanded testing and treatment and established public health standards; launched a vaccination campaign; supported reopening of schools; addressed inequities of COVID-19 response; and rejoined the World Health Organization. President Biden had initially set a goal of 1 million vaccinations a day by his first 100 days in office and later increased the goal to 1.5 million a day. The Biden administration also increased the number of doses being shipped weekly to states, purchased additional doses from Pfizer-BioNTech and Moderna, and rolled out new programs to increase access at select pharmacies and community health centers.
The federal government has left logistical decisions about distribution of vaccines to state governments. In December 2020, the CDC Advisory Committee on Immunization Practices (ACIP) recommended a phased allocation of COVID-19 vaccines, but official allocation was ultimately left up to the states. The CDC recommends healthcare personnel and residents of long-term care facilities receive first access to the vaccines (Phase 1a), followed by those who are 65 years and older, those 16–18 (depending on vaccine) to 64 years who have comorbidities, and frontline essential workers who are not healthcare workers (Phase 1b, vaccination eligibility in this phase was expanded in January 2021). Phase 2 includes people 16 and older who do not fit into the criteria for Phase 1. The ACIP did not make recommendations for people younger than 16. States and local jurisdictions might adopt different vaccine rollout criteria.
In addition to the Pfizer-BioNTech and Moderna vaccines, a number of other vaccine candidates are in development and testing. In late January, Janssen (a pharmaceutical company of Johnson & Johnson) announced positive topline efficacy and safety data for its single-shot COVID vaccine. According to the company’s press release, the Janssen vaccine was 72% effective in the U.S. and 66% effective overall in preventing moderate to severe COVID-19; it was 85% effective overall in preventing severe disease. Unlike the Pfizer-BioNTech and Moderna vaccines, the Janssen one is not an mRNA vaccine. The Janssen vaccine uses an adenovirus to carry a coronavirus gene into host cells to produce the coronavirus spike protein, which can help “prime” the immune system, Mathai Mammen, MD, PhD, Global Head, Janssen Research & Development, Johnson & Johnson, explained in an employee spotlight on the Johnson & Johnson website.1 Johnson & Johnson filed for emergency use approval in early February; it began review though was not yet authorized by the FDA at the time of this publication.
In February, AstraZeneca announced preliminary results from the Phase 3 clinical trial of its COVID-19 vaccine, finding 76% efficacy in preventing severe cases and hospitalizations of COVID-19 after the first dose and up to 82% efficacy with the second dose at a 12-week or more dose interval.2 The data showed a 67% reduction in positive PCR readings after a single dose, suggesting its potential to reduce asymptomatic virus transmission. At the time of this publication, the study had not yet been peer reviewed, and scientists interviewed by the New York Times wrote that more data analysis is needed.3
Several vaccines were approved for use in other countries. On its Coronavirus Vaccine Tracker, the New York Times reported that as of February 23, there were 20 vaccines in large-scale Phase 3 clinical trials, 27 were in Phase 2 expanded safety trials, and 41 were in the Phase 1 stage of testing safety and dosage.4


1. Levine H. COVID-19 update: Your latest questions about Johnson & Johnson’s investigational vaccine candidate answered. Johnson & Johnson. Jan. 5, 2021.
2. AstraZeneca. COVID-19 vaccine AstraZeneca confirms 100% protection against severe disease, hospitalisation and death in the primary analysis of Phase III trials. Feb. 3, 2021.
3. Santora M, Robbins R. The AstraZeneca vaccine may slow transmission of the virus. New York Times. 2021.
4. Zimmer C, et al. Coronavirus Vaccine Tracker. New York Times. Accessed Feb. 8, 2021.

Update on COVID-19 vaccines Update on COVID-19 vaccines
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