Equine inﬂuenza vaccine in China: Current status and challenges
Equine inﬂuenza (EI) is a major infectious respiratory disease caused by
equine inﬂuenza A virus (IAV). China has experienced four major EI
outbreaks, in 1974, 1989~1990, 1994 and 2007–2008 . The last EI
outbreak in China ﬁrst occurred in Xinjiang Province, Northwest China, in
November 2007. Then, the epidemic spread quickly to six other provinces
in northern China, central China and southern China within a year (Fig 1).
Since 2007, the predominant equine IAV strains in China have been H3N8
subtype strains belonging to Florida clade 2 [2,3].
Equids have a critical economic role in China. According to ofﬁcial
statistics from 2016, there are around 12 million (5.5 million horses,
4.6 million donkeys and 1.9 million mules) in Mainland China (http://www.
stats.gov.cn/tjsj/ndsj/2017/indexch.htm). Vaccination is an effective strategy
to prevent and control EI. However, EI vaccine development and regular
vaccination in equids is still a challenge in China.
China has not produced its own commercially available EI vaccine
containing the prevalent ﬁeld strain. After the third EI outbreak in 1994,
there was no large scale EI outbreak in China until the fourth occurred
13 years later. Thus, EI vaccines was not a research priority in China during
this period. Since 2007, researchers in China have been developing EI
vaccines based on the strains from the 2007–2008 outbreak and these
include inactivated, fowlpox virus-vectored attenuated live, subunit vaccine
and DNA vaccines . However, all these vaccines remain in development
and none are registered for sale.
Equine IAV evolves constantly. The World Organisation for Animal Health
(OIE) Expert Surveillance Panel on EI vaccine composition regularly
estimates the protective efﬁciency of the vaccine strain and gives
recommendations on updating vaccine composition (http://www.oie.int/
influenza/). Several amino acid changes in the haemagglutinin antigenic
sites were observed in the Chinese strains circulating in 2017,
compared with the strains isolated in 2007–2008 . This raises
concerns about whether the EI vaccines under development in China
will protect equines from infection with the prevalent strains. If the EI
vaccines currently in development in China do not have adequate
protective effects, it will be necessary to develop vaccines using the
latest and most prevalent equine IAV strain, instead of a virus that
circulated about 10 years ago. Continuous epidemiological surveillance
on equine IAV and estimation of the possible antigenic drift of prevalent
equine IAV strains is necessary. Furthermore, some EI vaccines under
development in China still rely upon aluminium salts as adjuvant .
Other recently developed adjuvants could help enhance immune
responses to speciﬁc antigens, generate more robust antibody levels in
equids, and have reduced side effects [5,6].
Another problem is the high cost of commercially available EI vaccines in
China. Many equine owners cannot afford routine vaccination against EI, and
this applies even for racehorses. Movement of unvaccinated, susceptible
racehorses from different geographical areas provides opportunities for
equine IAV transmission and EI outbreaks . Reducing the production and
transportation cost of commercial EI vaccines may also increase vaccine
uptake and reduce the number of susceptible equids in China.
Authors’ declaration of interests
The authors have declared no competing interests.
Sources of funding
This work was supported by Guangdong Natural Science Foundation
(2017A030310367), Postdoctoral Science Foundation of China
(2017M622716), and Guangdong Provincial Key Laboratory of Prevention
and Control for Severe Clinical Animal Diseases (2017B030314142).
Gang Lu collected data, analysed data and drafted the article. Guihong
Zhang and Shoujun Li designed the study and critically reviewed the article.
All authors gave their ﬁnal approval of the article.
Inner Mongolia 2008/02
Fig 1: The map of the affected provinces and the potential transmission routes of equine inﬂuenza A virus during 2007–2008 equine inﬂuenza outbreak in China. The
provinces and dates (year/month) of equine inﬂuenza outbreaks are indicated.
Equine Veterinary Journal 50 (2018) 544–545 © 2018 EVJ Ltd
Equine Veterinary Journal ISSN 0425-1644